Polyvinyl chloride (PVC) and polyolefin (PO) are economical thermoplastics that can be extruded into many useful articles. Unfortunately, PVC and polyolefin articles discolor, lose gloss, become chalky in appearance and embrittle if exposed to sunlight for extended periods of time. The discoloration and embrittlement is especially detrimental for articles intended for long-term weather exposure, such as house siding, window frames, rain systems, soffits, trim, pipe, panels, etc.
Many approaches have been used to improve the performance of the PVC and PO articles. Stabilizer systems such as lead stabilizers, calcium-zinc stabilizers, and the use of high levels of titanium dioxide pigment have be employed in the PVC resin.
An alternative method has been to employ a thin weatherable capstock over the PVC or PO substrate applied as a laminate or by co-extrusion. The capstock may be stabilized PVC, or a non-PVC polymer. Acrylics have been favored as capstocks for their color stability in outdoor exposure, however they are higher in cost. Film laminates of polyvinylidene difluoride have also been used. Several patents which describe the use of weatherable laminates for rigid PVC substrate compositions include EP 1061100; EP 0473379; U.S. Pat. Nos. 4,141,935; 4,169,180; 4,183,777, 5,306,548; and 5,976,671.
The problem with capstock and laminate processes is that they require a second piece of extrusion or laminating equipment that the throughput rates must be matched to account for differential cooling. Additionally, there is a significant loss of time and material wastage when the production line switches from one color to another. A further difficulty arises in the production/fabrication of dark colored PVC or PO articles, as the slower heat dissipation from the formed article causes production issues as well as occasional failure in the field (delamination, embrittlement, color loss, gloss loss, chalking).
U.S. Pat. No. 5,972,514 describes a means of coating a PVC substrate with a polymer coating using an air or airless spray, or an electrostatic process. The coating is then crosslinked by IR radiation.
Inkjet printing onto non-absorbant plastic substrates, such as transparencies, is known in the art, such as in U.S. Pat. No. 5,555,006.
KYNAR polyvinylidene coatings are formed onto flexible PVC by means of lamination of a pre-printed, pre-coated or clear PVDF flexible film.
There is a need for a better in-line method of forming a weatherable protective coating onto a rigid PVC or PO substrate.
Surprisingly it has been found that a weatherable protective coating can be formed onto a PVC or polyolefin extruded substrate by the in-line application of a polymeric solution or suspension by means of inkjet, brush-coat, roll-coat, gravure printing, flexographic printing, thermal transfer printing or spray application. A further advantage of inline coating application by any of these methods is that color designs are easily created and readily customized or adjusted or matched on the extruded PVC or polyolefin.